Image defogging is a technique for removing fog in a foggy image to make image contents more visible. However, a defogged image obtained by defogging processing usually is relatively dark, and contents in the defogged image sometimes are not visible enough for a person to clearly recognize. Therefore, the exposure of the defogged image needs to be enhanced.
Currently, there exist the following two exposure enhancement methods for the defogged image:
The first method is an image transforming method based on pixel intensity values. The method includes log transformation, gamma transformation, and piecewise linear transformation. The log transformation and the gamma transformation need complex operations, and much computation time is needed. The piecewise linear transformation cannot provide a continuous transformation function, leading to the obtained result not ideal.
The second method is an image transforming method based on histogram transformation. The method firstly computes the histogram of an input image, and then performs histogram equalization and histogram matching, etc. The effect of the resultant image obtained by the method is very bad, and almost all noises are shown. In addition, it is difficult to implement the image transformation method based on histogram transformation in parallel.